Abstract: A duct seal for sealing a duct (4) to a substrate (20) such as a feedthrough comprises a sealing member (6), a biasing member (8), such as a wrapped spring sheet and an insert (12) positioned between the substrate (20) and the sealing member (6). The biasing member (8) can be operated, through the insert (12) from the outside of the duct. When the substrate is a feedthrough (20), for example, it is advantageous that the biasing member (8) is operated through the insert rather than through the feedthrough (20) itself, since it allows the feedthrough to be temporarily sealed against contaminants.